A loudspeaker is an electromechanical device that converts an electrical signal into sound. There are numerous types of conventional loudspeakers. Among the more common type of loudspeakers, is a loudspeaker comprising a driver that is coupled to an enclosure and/or baffle. The driver vibrates in response to an electrical signal, thereby producing front and rear sound waves. Some drivers are specifically designed to reproduce the sound for a particular range of frequencies. For example, some drivers are designed to produce mid or low frequencies while others are designed to reproduce the upper frequency range. Often these various drivers are used together in a single loudspeaker. When used together, these various drivers may be augmented through the use of crossover electronic elements, serving to divide the frequencies sent to each driver from an input source. The purpose of the enclosure or baffle is to provide a mounting area as well as separate the front and rear sound waves to provide a usable and wide frequency response. Without an enclosure or large baffle, the front and rear sound waves will combine destructively, making the output sound, particularly in the low frequencies, virtually inaudible. It is therefore then the goal of the loudspeaker enclosure to control the front and rear waves such that they combine in a constructive fashion, reinforcing frequencies and output sounds that are not reproduced by one wave or the other exclusively, or not combine at all.
One type of loudspeaker implements a “finite baffle” design. In a “finite baffle” design, direct radiating loudspeakers are mounted to a surface facing the listening position. The finite baffle is a board or similar structure, typically of several meters in width and height, to which the loudspeaker is affixed. The finite baffle is used to separate the front and rear waves of the loudspeaker. A loudspeaker based on a finite baffle design is a non-resonant design, whereby the air propagation of the cone is not harnessed in an enclosure, and the air volume of the enclosure is not utilized to damp the cone of the loudspeaker. Nevertheless. This design is noted for producing an open sound, but is limited in power handling, sound pressure (decibel) output, and excessive size, In addition, this design can only be fully realized indoors, and is strongly reliant on the effect of room placement and coupling.
Another type of loudspeaker separates the front and rear sound waves by virtue of a sealed enclosure, wherein the rear wave is confined within the enclosure, serving to reinforce the cone of the driver acting as an air spring. This is often called acoustic suspension or the “infinite baffle”. This compact design, while easy to build and tune, is notoriously inefficient, limits low bass frequencies. This design can produce unwanted panel resonances or reflections within the enclosure that can be reflected back through the driver as well as non-linearities in the driver itself caused by the high air pressure changes in the enclosure. Other designs include the features of the acoustic suspension, but use an enclosure opening (port) sometimes including a tube or slot (a Helmholtz resonator) or a passive radiator driver to reinforce the front wave, allowing low frequencies to emanate from the port or radiator and dampen the driver at its resonance frequency. The tuning of these enclosures is known and can be reproduced through a defined formula. These designs are limited in producing a free and natural bass response, especially in the upper and mid bass regions, and produce unwanted panel resonances and standing waves. Still another design is set forth in U.S. Pat. No. 4,628,528 to Bose et al. suggests a waveguide enclosure (transmission line) whose length is determined by a formula of ¼ the wavelength of the chosen driver's resonance frequency, is designed as a labyrinth, and is typically constructed with an average cross sectional area 1.5-3.0 times the size of the driver. Extensive acoustical stuffing material is utilized for tuning purposes. The purpose of “stuffing” is to destroy unwanted high and middle frequencies from emanating from the rear wave and out an enclosure opening (port), where only low frequencies will exit, and recombine constructively with the front wave. “Stuffing”, however; creates manufacturing problems related to repeatability, loss of efficiency, and tuning reliability issues if the stuffing moves inside the enclosure. U.S. Pat. No. 6,700,984 to Holberg et al. suggests that the use of a transmission line enclosure with non-linearly tapering walls, with largest diameter near the driver and smallest diameter near the enclosure opening. It also recommends tuning based on U.S. Pat. No. 4,628,528 to Bose et al., discussed above, wherein the length of the enclosure is determined initially by a ¼ wavelength of the desired tuning frequency, with final tuning done by adding acoustical fibers (stuffing) packed into the enclosure. This design has numerous acoustical advantages over the aforementioned designs, one being the elimination of panel resonances reflecting from the enclosure and back through the driver itself, which can produce unwanted distortion and phasing issues.
All of these designs call for a front baffle with diameter or area greater than the area of the driver itself. Inherent with a baffle is baffle losses, produced when the front sound wave bounces off the enclosure and/or the enclosure sides and is projected towards the listener, out of phase with the desired sound wave. Baffles can also limit, filter, and/or destruct the output of certain frequencies measured “off axis,” most commonly 30 degrees to either side of the reference loudspeaker. The published work of engineer H. F. Olson from around 1969 is often referenced for baffle diffraction effects. The results of the research suggests the use of baffles shaped as spheres or enclosure sides progressively angled away from the driver and avoiding any 90 degree angles. All of his examples assume the baffle is substantially greater in area than the actual width of the drivers themselves, however.
Loudspeakers by their very nature are compromises; with no one design embodying all of the desired characteristics of the listener. It is therefore the object of this invention to improve upon existing and previously discussed prior art. Accordingly, there is a need for an improved loudspeaker that overcomes the above disadvantages.